Fancy effects: fix fireworks effect positioning

As discussed in a matrix room previously:

PureTryOut (matrix.org): aa13q not sure if you noticed, but the 🎆 effect seems to only happen from left to middle of the timeline. The right side never gets an effect for whatever reason

aa13q: True, found it, but didnt managed to fix yet. Looks like effects container is moved to left and missing left sidebar size. Not happeng when sidebar is hidden

Fixing the emitted object parent from root to parent is fixing the bug.